Our complete pump rebuild kit for the Hypro D503 is more extensive than the standard repair kits. It is basically 2 Hypro kits (9910-KIT1881 and 9910-KIT1987) plus the sight glass o-ring. Our kit includes all the valves, as well as the o-rings and diaphragms.

Hypro D503 Repair Kit includes:

3 x 9910-620085 Diaphragms

6 x 9910-1409050 Valves

1 x 9910-390180 O-ring

6 x 9910-620030 O-rings

6 x 9910-540361 O-rings

6 x 9910-480440 O-rings

On the D503, when you are changing the valves, you will find 2 o-rings on the valve and 2 o-rings on the head assembly near the diaphragms.

If your Hypro D503 (or the D503GRGI which includes the gearbox and pressure regulator) has milky grey oil in the oil sight glass, you have mixed oil in the crankcase and likely a broken diaphragm. You must change your diaphragms before using your pump. Using a D503 with mixed oil can destroy your pump.